Frequency-changing circuit



PinfedgJsn. '21, 1942 2,271,418 FaEQunNcY-CnANGiNG CIRCUIT 'Charles' Cecil Eaglesiield, Surrey, England, assignor, by mesne assignments, to Radio Corpo ration of America, New York,

tion of Delaware N. Y., a corporav Applicaun June 13, 1939, serial No. 218,814

In` Great Britain October Z6, 1938 "s claims. (c1. 17a-5.8)

This invention relates to frequency-changing circuits employing electron discharge tubes and has for its object to provide an arrangement exhibiting high conversiony conductance ers)- by making use of a' secondary-emission tube, i. e. a tube incorporating a primary cathode,

-a control grid, a secondary emission electrode (hereinafter termed the auxiliary cathode) which gives off secondary electrons when bombarded with primary electrons, and an anode, with or without other electrodes such as a screen grid.

The invention is based on recognition of the fact that with a suitably constructed tube of this type oscillations may be produced, and the anode stream modulated accordingly, by coupling the control grid and the auxiliary. cathode; in

such a tube the alternating voltages of the con-1l trol grid and auxiliary cathode are normally in phase and if a coupling circuit is provided between these electrodes s o as to preserve-or substantially preserve this relationship, (the phase agreement needvnot be at all exact) the tube will act as a generator of oscillations.

According to the present invention provision is made of a self-oscillating frequencychanger comprising a secondary emission tube provided with a coupling as described-in the preceding paragraph, the signal 4input circuit-being con- 30 nected to the control grid, the oscillation generated being such as to modulate the anode stream at the desired heterodyne frequency, and

-the anode circuit being provided with an impedance from which the intermediate frequency 35 is derived.

In order that the inventionmay'be vmore readily understood reference will now be made to the embodiment thereof that is illustrated by Way of example in the accompanying drawing. 40

The drawing shows a self-oscillating frequencyv changer for a television receiver comprising a secondary emission tube V. This tube has an indirectly heated cathode I, a control grid 2, a screen grid 3, an auxiliary cathode 4 and an anode 5. The control grid 2 is connected to the input terminal 6 by way of a coupling condenser C1 and the lower end of the bias resistance R1 connected into the cathode lead is joined to the input terminal 1. the usual by-pass condenser Cz;V The grid-cath ode circuit is shunted by a variable inductance L1 which in conjunction with the grid-cathode capacity tunes the input circuit tothe signal fre- (and I therefore suitable inter alia for television receivas compared with variable capacity tuning that high grid impedance at the heterodyne frequencyA is maintained.

The screen grid 3, the auxiliary cathode 4 and the 4anode 5 are connected to the positive side of the power supply by decoupling resistances Rz,

r R3 and R4 with which are associated decoupling condensers Cs, C4 and C5 respectively. The connection between the lauxiliary cathode 4 and the associated decoupling resistance R3 includes a parallel circuit of inductance L2 and capacity C6 tuned to the heterodyne frequency, e. g. 32 megacycles/sec. The end of this tunedvcircuit remote from the auxiliary cathode 4 is connected to the cathode l by a resistance R5 and the inductance La has a tapping, e. g. a central tapping which is connected to the control grid 2 by a condenser C1 anda resistance Re in series. Since thegrid -2k and auxiliary cathode '4 are in phase the coupling of thesetwo electrodes by means of the resistance Rs causes the tube to self-oscillate. The condenser C1 is merely a blocking condenser to prevent the application of the high positive voltage to the grid 2.`

The anode circuit includes the primary La of a band-pass transformer across which the Vision intermediate frequency is developed and a variable inductance L4 across whichthe sound intermediate frequency is developed. The secondary L5 of the'band-pass transformer is connected to a terminal 8 from which the vvision intermediby a condenser Cs.

able choice of capacity values this 's1\.rra`.1 1gement Resistance R1 is shunted byfjv 50 ate-frequency circuit is supplied while 'the inductance L1 is connected through a coupling condenser Cs'to a terminal 9 from which the sound intermediate-frequency circuit is sup-- plied. The input to the latter circuit is shunted It is found that with a suitpermits the sound and vision intermediate-frequency circuits to be tuned independently of one another. The inductances'La, Le are shunted -by condensers'Cm, C11 and damping resistances Rs, R9 respectively. The voltage of the screen 3 should be apprecif ably lower than the lowest voltage to which the auxiliary cathode 4 swings.

With the above-described resistance coupling factory results in practice and is sinple to adjust. A circuit that produces a'- phase relation.

that is nearer to that whichvis theoretically the quency. This arrangement offers the advantage 55 optimum is produced by replacing the resistance Rs by an inductance; this circuit may be afppropriately used when the heterodyne frequency is lower than the signal frequency. Other forms of coupling may be used; for example. when the heterodyne frequency is higher than the signal frequency the coupling may be effected solely by a condenser. The connection to the circuit Lrz,'Cs maybe eiected v4at theend remote from the auxiliary cathode instead of at a tapping asv shown.

The invention-05ers the advantage as compared 1 with the use of a secondary emission tube operating as a'dynatron oscillator that a circuit of high impedance is not required in the connection to the auxiliary` cathode; furthermore since a high impedance circuit is not required we may use a circuit consisting of high C and low L whereby the behavior of the tube at frequencies other than the heterodyne frequency (in particular the intermediate frequency) is not appreciably aiected by the insertion of the components necessary for l self-oscillation.

I-claim:

1. A frequency changer network comprising an electron discharge tube having at least a primary cathode, a signal input electrode, an auxiliary cathode and an anode, a signal input circuit connected between the input electrode and the primary cathode, a local oscillation circuit resonantv to a frequency different from the signal input circuit connected between the auxiliary cathode and the primary a. tap on the inductance of the oscillation circuit, and an impedance included in the anode cir.

- 'mary cathode,'a signal' input electrode, an auxiliary cathodeand an anode, a signal input circuitv connected between the input electrode and the primary cathode, `an oscillation' circuit resonant to a frequency different from the signal input circuit having its high potential end connected to the auxiliary cathode, a resistance connected between the low rpotentialend of said oscillation circuitand the primary cathode, a

circuit including a series resistance and a condenser connected between the input electrode and a tap on` the inductance of the oscillation circuit, and an impedance included inthe anode circuit from across which the intermediate frequency is derived.

CHARLES CECIL EAGLESFIELD.

cathode, a path including animpedance connected between the input electrode and, 

